1. Field of the Invention
The present invention relates to a head chip that ejects liquid from a nozzle opening to record an image or a character on a recording medium, a liquid jet head having the head chip, and a liquid jet device having the liquid jet head.
2. Description of the Related Art
At present, as one of liquid jet device, there has been provided an ink jet type recording device that ejects ink (liquid) on a recording medium such as recording paper for recording an image or a character thereon. The recording device is, for example, a printer, a facsimile machine, and so on. The recording device supplies ink to an ink jet head from an ink tank through an ink supply pipe, and ejects ink onto the recording medium from a nozzle opening of the ink jet head, thereby performing the recording.
In general, as illustrated in FIGS. 12 and 13, the ink jet head is equipped with a head chip 100 including an actuator plate 101, a cover plate 102, a nozzle plate 103, and a support plate 104.
The actuator plate 101 is a plate made of a piezoelectric material, and has a plurality of grooves 111 partitioned by side walls 110, respectively. The grooves 111 function as channels into which ink flows to be accumulated. Plate-like drive electrodes (not shown) are formed on both side walls 110 of each groove 111 along the longitudinal direction thereof by vapor deposition. A drive voltage is applied to the drive electrodes.
The cover plate 102 is stacked on an upper surface of the actuator plate 101, and shields the plurality of grooves 111. An ink introduction aperture 102a into which ink is introduced is recessed in the cover plate 102. With the configuration, ink is introduced into the plurality of grooves 111.
The actuator plate 101 and the cover plate 102 which are stacked on each other are supported by the support plate 104 in a state where those plates 101 and 102 are fitted into a fitting aperture 104a of the support plate 104. In this situation, an end surface of the support plate 104 is flush with end surfaces of the actuator plate 101 and the cover plate 102.
The nozzle plate 103 is in the form of a plate, and fixed to the end surfaces of the support plate 104, the actuator plate 101, and the cover plate 102 with an adhesive S. The adhesive S is omitted from FIGS. 12 and 13.
The nozzle plate 103 has a plurality of nozzle openings 103a formed at given intervals. In this case, the plurality of nozzle openings 103a are formed to communicate with the plurality of grooves 111, respectively. That is, the nozzle openings 103a are formed at the same intervals as the pitches of the grooves 111.
Further, it is general that each nozzle opening 103a is formed with a tapered cross section where the diameter of an inlet on the groove 111 side is larger than the diameter of an outlet on the recording medium side.
When ink is ejected from the ink jet head having the head chip 100 thus configured, ink is first supplied into the plurality of grooves 111 through the ink introduction aperture 102a, and filled therein in advance. Then, a drive voltage is applied to the drive electrodes. As a result, the side walls 110 of the actuator plate 101 are deformed due to the piezoelectric thickness-shear effect. The deformation of the side walls 110 and the drive method are described in more detail. First, the side walls 110 on both sides of each groove 111 from which ink is ejected are so deformed as to project toward the groove 111 sides adjacent to the ejecting groove 111. That is, the ejecting groove 111 is deformed as if the ejecting groove 111 were swelled. Then, the volume of the ejecting groove 111 increases, and hence ink is led into the groove 111 from the ink introduction aperture 102a. After ink has been led into the ejecting groove 111, the drive voltage applied to the drive electrodes is set to zero. As a result, the volume of the groove 111 which has increased once returns to its original volume. Through the above-mentioned operation, an inner pressure of the ejecting groove 111 increases to pressurize ink. As a result, a drop of ink, that is, ink droplet can be ejected from the nozzle opening 103a. 
Incidentally, in order to perform more downsizing and higher image quality, future head chips are expected to have narrower intervals (pitches) between the grooves 111. Specifically, it is desirable that the existing design with horizontal width of the grooves 111 of about 70 to 80 μm and horizontal width of the side walls 110 of about 60 to 70 μm be narrowed to a design with horizontal width of the grooves 111 of about 40 μm and horizontal width of the side walls 110 of about 30 μm for narrowing the pitches.
In the size of the nozzle openings 103a, currently, the inlet diameter is 50 to 55 μm, and the outlet diameter is 20 to 40 μm. Even if the pitches are to be narrowed, it is difficult to further reduce the above-mentioned size in order to ensure the ejecting performance of ink. For that reason, as illustrated in FIG. 14, when the pitches are to be narrowed, the inlet diameter of the nozzle opening 103a becomes larger than the horizontal width of the groove 111.
When the pitches are to be narrowed in the conventional head chip, there arise the following disadvantages.
In normally assembling the head chip 100, the nozzle plate 103 is bonded to the support plate 104, the actuator plate 101, and the cover plate 102 which are coated with the adhesive S. For that reason, in bonding those members, there arises a disadvantage that the adhesive S is caused to flow into the nozzle openings 103a, and blocks a part of the nozzle openings 103a. 
In particular, with the inlet diameter of the nozzle openings 103a being larger than the horizontal width of the grooves 111 as described above, the adhesive S is liable to flow into the nozzle openings 103a as illustrated in FIGS. 15 and 16. Thus, the probability that the nozzle openings 103a are blocked is high.
When a part of the nozzle openings 103a is thus blocked by inflow of the adhesive S, ejection failure in which ink cannot be normally ejected is induced. For that reason, it is desirable to take some countermeasures so as to prevent the above-mentioned disadvantages.
Under the above-mentioned circumstances, as one of the countermeasures, there has been known a method of stepping the adhesive for adhesion of the nozzle plate (JP 05-330061 A). In the method, the nozzle openings are formed in the nozzle plate having an adhesive surface coated with the adhesive in advance. Then, the adhesive around the nozzle openings is concentrically removed with a diameter larger than the diameter of the nozzle openings.
As another countermeasure, there has been known a method of forming a plurality of grooves for complementing a surplus of the adhesive around the nozzle openings when the nozzle openings are formed in the nozzle plate (JP 07-117230 A).
However, the conventional method still suffers from the following disadvantages.
First, according to the method of stepping the adhesive, it is conceivable to prevent the adhesive from flowing into the nozzle openings. However, it is difficult to find out a suitable adhesive for the stepping method. That is, the adhesive of this type is required to provide at least an adhesion property for firmly adhering to the nozzle plate, a shaping property for executing the stepping process, and ink resistance. However, it is difficult to actually find out the adhesive having those various properties, which makes the method unviable.
On the other hand, according to the method of forming a plurality of grooves for complementing a surplus of the adhesive around the nozzle openings, the surplus adhesive can be indeed pulled into the grooves. However, the adhesive coated at positions close to the nozzle openings is still caused to flow into the nozzle openings. Further, when the surplus adhesive fills the grooves, and the remaining surplus adhesive cannot be complemented by the grooves, the surplus adhesive is still caused to flow into the nozzle openings. For that reason, the amount of inflow adhesive can be indeed reduced, but inflow per se cannot be prevented. Accordingly, the possibility that the ejection failure is induced still remains.
Further, there is conceivable a technique in which, for the purpose of preventing the surplus adhesive from being contained, the adhesive having the amount smaller than the amount for sufficient adhesion is coated to allow the nozzle plate 103 to adhere to a joining body formed of the actuator plate 101 and the cover plate 102. However, when the above-mentioned technique is applied, there is the fear that the adhesion is insufficient. When the adhesion is insufficient, the following disadvantages may occur.
For example, in the case where the adhesion is insufficient, when the nozzle plate 103 is cleaned up by a cleaning member such as a wiper (not shown), there is a risk that the nozzle plate 103 may be peeled off the above-mentioned joining body. Further, when the adhesion is insufficient, there is a risk that an unwanted gap may be formed between the nozzle plate 103 and the joining body, whereby the ink led to the ejecting groove 111 is leaked out of the gap.
In this way, when the adhesive is insufficient, the fear may arise that the above-mentioned disadvantages occur. Therefore, it is essential to apply the sufficient amount of adhesive, and it is necessary to allow the nozzle plate 103 to surely adhere to the joining body. Accordingly, there arises the above-mentioned problem which is resulting from the adhesive.